The present invention relates to packetized data networks, and more particularly, to measuring the packet jitter characteristics of packetized data networks.
The invention measures the jitter (also referred to herein as “packet jitter”) of TCP connections or UDP streams without altering the behavior of the network. This type of non-intrusive measurement is also referred to herein as a “passive measurement.”
Packet jitter is an important characteristic of real-time traffic flows such as VoIP or streaming media (e.g., video). High jitter can often lead to poor quality of the media stream. Jitter is the overwhelming cause of poor quality in VoIP applications. Packet jitter is related to packet delay, and can best be described as a variation in packet delay. In a packet switched network, not all packets experience uniform delay across the network. Packets may take different paths between the same network endpoints. Further, routers and other network components may introduce variable delays as a result of congestion and other factors. Jitter can occur in a public network when an intermediate switch along the network path is busy with another unrelated packet. When this occurs, the second packet is held at the switch until transmission of the first packet is complete. The amount of delay is variable and unpredictable, since packets typically vary in length. If the jitter exceeds the ability of the receiving device to compensate through buffering, voice quality will suffer or the signal will be completely obliterated. The ability to passively measure the jitter of any type of UDP or TCP flow can provide network operators valuable information about the performance of their networks, and assist them in troubleshooting network issues.
In prior art systems, the jitter of a network may be measured by performing an active measurement, i.e., measuring the jitter of packets that the test itself injects into the network. One disadvantage to this configuration is that the injected test packets of an active measurement may alter the behavior of the network under test, thus skewing the results. Another disadvantage is that the network may treat test packets differently than “real” packets, such as packets within an H.323 voice over IP stream.
It is an object of the present invention to substantially overcome the above-identified disadvantages and drawbacks of the prior art.